1. Field of the Invention
The present invention relates to a brake system of a vehicle, and more particularly, to a brake system of a vehicle constructed to execute an automatic behavior control of the vehicle such as a spin control or a driftout control according to running conditions of the vehicle such as vehicle speed, lateral acceleration, yaw rate, steering angle, longitudinal acceleration and wheel speeds, and also to execute a calculated braking control of the vehicle according to a depression of a brake pedal by the driver.
2. Description of the Prior Art
There have been proposed various automatic behavior control systems for vehicles constructed to execute a spin control or a driftout control by automatically braking a selected one or more of the front left, front right, rear left and rear right wheels according to behavior control calculations based upon running parameters of the vehicle such as vehicle speed, lateral acceleration, yaw rate, steering angle, longitudinal acceleration, and wheel speeds, as shown in, for example, U.S. Pat. No. 5,717,591/DE-OS 19533575, U.S. Ser. No. 08/680,044/DE-OS 19632068, U.S. Pat. No. 5,727,853/DE-OS 19644293, and U.S. Ser. No. 08/798,465/DE-OS 19707059.
According to those prior art brake systems, during a normal running of the vehicle where there is no need of spin or driftout control, the wheel cylinders of the vehicle are generally connected with the master cylinder adapted to be actuated by a driver through a depression of the brake pedal, while when it is judged by an automatic controller, indeed a microcomputer, incorporated in the brake system that there is a need of a spin control or a driftout control, a pertinent one or more of the wheel cylinders are disconnected from the master cylinder so as to be be selectively supplied with a fluid pressure of a powered fluid pressure source such as a motor-driven pump via a control valve or valves operated by the automatic controller according to a behavior control calculation conducted therein based upon running parameters of the vehicle such as the vehicle speed, etc.
As well known in the art, a spin control by such an automatic brake system is generally executed so as to supply a controlled fluid pressure to the wheel cylinder of a front wheel serving at the outside of a turn running of the vehicle from the view point of most effectively generating an anti-spin moment in the vehicle by its inertia, while a driftout suppress control is executable in higher variety of manners, so as to supply a controlled fluid pressure to the wheel cylinder or either of both of the rear wheels principally from the view point of decelerating the vehicle, as the driftout is generally caused by an overdue of the centrifugal force against the tire grip force available at the front wheels, or to supply a controlled fluid pressure to the wheel cylinder of a rear wheel or rear as well as front wheels serving at the inside of a turn, so as to generate an anti-driftout moment in the vehicle.
In either case, if the brake system is so constructed that, when one of the left and right side wheel cylinders is disconnected from the master cylinder for a behavior control, the other wheel cylinder is maintained in communication with the master cylinder, the driver's will for optionally braking the vehicle is executed through the other side wheel cylinder. Indeed, when, for example, the front right wheel is braked for the purpose of suppressing a spin of a vehicle making a left turn, a spin control is executed according to a spin control calculation which calculates a due slip ratio to be effected at the front right wheel based upon a reference wheel speed which is generally selected to be the wheel speed of the front left wheel. Therefore, when the driver depresses the brake pedal during an execution of an automatic spin control, or when an automatic spin control is executed while the driver is depressing the brake pedal, the driver's will for a deceleration of the vehicle is executed at least by the front left wheel, while the automatic spin control is executed in reflection of the deceleration of the vehicle according to the driver's will through a reduction of the reference wheel speed. Since the wheel speed of the front wheel serving at the inside of a turn is generally used as the reference wheel speed also for the driftout control, the same effect of reflection of the driver's braking is also available in the driftout control.